The present invention relates to a disposal of radio-active wastes and, more particularly, to a method of producing radio-active waste package which affords a safe disposal of the radio active wastes to the natural environment. The invention is further concerned with an apparatus for producing the above-mentioned radio-active waste package.
The radio-active wastes from boiling water reactors (BWR) nuclear power station or the like plants are stored in a shielded container over a predetermined period, in order to attenuate the radio-activity. The total volume to be stored is impractically large, because the waste of this kind is in the liquid state. It is therefore a common measure to solidify the liquid waste.
A practical method for solidifying the liquid waste is to fill a vessel with the radio-active waste liquid, and evaporating the water content so as to solidify the radio-active waste in the vessel. This method, however, can provide only a small efficiency of use of the vessel, because the radio-active waste after the solidification occupies only a small part of the volume in the vessel, even when the vessel is completely filled with the liquid waste before the solidification.
It is also proposed and practised to fill each vessel completely full with separately solidified radio-active waste. In order to obtain a radio-active waste package which can be disposed to natural environment after a storage over a predetermined period, it is necessary to adjust the amount of the radio-active waste such that the requirement of regulation for final disposal of radio-active waste is fully met. Such an adjustment is difficult especially when the radio-active waste is in the liquid state.
To overcome above-stated problems, Japanese Patent Laid-Open Publication No. 34200/1977 discloses the formation of pellets from the radio-active waste after the solidification. More specifically, in this Patent Laid-Open Publication, disclosed is a method for disposing of the radio-active waste comprising the steps of evaporating the radio-active waste liquid in a membrane type evaporator, forming pellets from the powders of radio-active waste obtained in said evaporator, and storing the pellets in a storage tank having a shielding construction. This proposed method considerably facilitates the adjustment of the amount of radio-active waste for fulfilling the regulation for the final disposal.
As a method of preparing a radio-active waste package which can be disposed to the natural environment, Japanese Patent Laid-Open Publication No. 85699/1977 discloses a method in which a drum is filled with the radio-active waste together with an asphalt material. In this package, the drum is provided at its central portion with a cage in which pellets of the radio-active waste are to be disposed, while the space surrounding the cage is adapted to be filled with the asphalt material.
This method, however, is still insufficient in that the mechanical strength of the package is not strong enough and, therefore, the package is liable to be damaged or broken when disposed to the natural environment, because the block of the pellets cannot be sufficiently impregnated with the asphalt material by a mere filling of the drum with the asphalt material. This problem of lack of strength of the radio-active waste package is serious especially when the packages are bound for offshore disposal.